Closed system


A closed system is a physical system that does not allow transfer of matter in or out of the system, though, in different contexts, such as physics, chemistry or engineering, the transfer of energy is or is not allowed.

In physics

In classical mechanics

In nonrelativistic classical mechanics, a closed system is a physical system that doesn't exchange any matter with its surroundings, and isn't subject to any net force whose source is external to the system. A closed system in classical mechanics would be equivalent to an isolated system in thermodynamics. Closed systems are often used to limit the factors that can affect the results of specific problem or experiment.

In thermodynamics

In thermodynamics, a closed system can exchange energy but not matter, with its surroundings.
An isolated system cannot exchange any heat, work, or matter with the surroundings, while an open system can exchange energy and matter.
For a simple system, with only one type of particle, a closed system amounts to a constant number of particles. However, for systems which are undergoing a chemical reaction, there may be all sorts of molecules being generated and destroyed by the reaction process. In this case, the fact that the system is closed is expressed by stating that the total number of each elemental atom is conserved, no matter what kind of molecule it may be a part of. Mathematically:
where is the number of j-type molecules, is the number of atoms of element i in molecule j and bi is the total number of atoms of element i in the system, which remains constant, since the system is closed. There will be one such equation for each different element in the system.
In thermodynamics, a closed system is important for solving complicated thermodynamic problems. It allows the elimination of some external factors that could alter the results of the experiment or problem thus simplifying it. A closed system can also be used in situations where thermodynamic equilibrium is required to simplify the situation.

In quantum physics

This equation, called Schrödinger's equation, describes the behavior of an isolated or closed quantum system, that is, by definition, a system which does not interchange information with another system. So if an isolated system is in some pure state |ψ ∈ H at time t, where H denotes the Hilbert space of the system, the time evolution of this state.
where is the imaginary unit, is the Planck constant divided by, the symbol indicates a partial derivative with respect to time, is the wave function of the quantum system, and is the Hamiltonian operator.

In chemistry

In chemistry, a closed system is where no reactants or products can escape, only heat can be exchanged freely. A closed system can be used when conducting chemical experiments where temperature is not a factor.

In engineering

In an engineering context, a closed system is a bound system, i.e. defined, in which every input is known and every resultant is known within a specific time.